Sample size calculations, using nQuery Advisor, assuming 15 minutes for a standard procedure, and 12 minutes for a prone procedure (common standard > deviation of 5 minutes); the difference in duration of 2 minutes has important public health implications and was considered clinically meaningful in other studies of modifications in Colonoscopy procedures (4,5,6,7,8,9). Using a two-tail alpha error of 0.05, and beta error of 0.10 (power >90% ), 60 patients in each arm would be required (120 total). The study would end if the target sample size is reached early.